Known screwdriving spindle assemblies include an electric or pneumatic motor for rotating a shaft whose end is fitted with a chuck device for holding caps. The shaft is also driven with vertical motion enabling the cap to be put into contact with and screwed onto a threaded neck.
One of the concerns relating to such spindle assemblies lies in controlling the tightening torque applied to the cap. It is important for the torque to be large enough to ensure that the package is properly closed and to avoid any untimely loosening of the cap while it is keeping the package closed, but without thereby obliging the user to make use of a tool for opening the package. A torque limiter device must therefore be interposed between the motor and the spindle shaft in order to transmit a determined tightening torque.
Friction-based torque limiter devices are known, in particular from documents U.S. Pat. No 4,756,137 and EP 387 153, which devices comprise two plates pressed one against the other. However the friction between the two plates gives rise to significant wear, and to heating, thereby altering their coefficients of friction. The transmitted tightening torque is therefore not constant. There also exist magnetic torque limiting devices that avoid the above-mentioned drawbacks. However, those devices suffer likewise from problems of adjusting torque, in particular because the magnetic elements age, and when permanent magnets are used, chattering occurs on sliding.